1. Field
The invention relates to apparatus and methods for mounting and interconnecting a Radio Frequency Integrated Circuit (RFIC) for automotive radar applications. More particularly, the invention relates to an interconnection apparatus and method for low cross-talk chip mounting for automotive radars.
2. Background
Many automotive designers and manufacturers are seeking to produce high-density microwave modules that achieve good isolation between circuit elements. In particular, transceiver applications (e.g., radar and communication RF front-ends) need to have good isolation to ensure receiver sensitivity and prevent leakage between channels.
Multilayer architectures incorporating complex circuits on a common substrate material pose some challenging isolation problems. For example, when circuits are printed on a common substrate, surface waves excited by planar discontinuities or leaky modes tend to induce parasitic currents on neighboring interconnects and circuits leading to unwanted interference. This parasitic coupling becomes increasingly more problematic as circuits are printed on multilayered structures for higher density and smaller size. In such multilayered structures, proximity effects are dependent on the interconnect geometry. The layout design and relative placement of lines, vias and vertical transitions should be carefully considered in order to reduce any unwanted interference.
Isolation becomes more important and more problematic at the connections to the RFIC chip since most of the signal transmission lines converge on a very small area (typically around 3×3 mm2) adjacent to the RFIC chip and are interconnected to the RFIC chip. Due to their close proximity, these signal transmission lines tend to interfere with one another causing deleterious effects on the radar performance. Furthermore, RFIC chips (e.g., SiGe BiCMOS and RF CMOS chips) tend to integrate multiple signal transmission lines (e.g., 4, 8 or 16) on a single chip, further emphasizing the need to have good isolation between the signal transmission lines.
FIG. 1 is a schematic view of a prior art 3D integrated radar RF front-end system 100 having antennas 105 that are combined together using transmission lines 110 on a liquid crystal polymer (LCP) substrate 120. The antennas 105 are printed on the front-side and the transmission lines 110 are printed on the backside. The transmission lines 110 are connected to an RFIC chip 115. The transmission lines 110 provide good performance in terms of loss and low crosstalk (i.e., every channel is completely isolated from the others and extremely low levels of crosstalk are achievable). Instead of using machined metallic waveguides, the transmission lines 110 are planar lines that are printed on the LCP substrate 120. The planar lines are microstrip lines at the topside and coplanar waveguides (CPW) at the backside.
The LCP substrate 120 may be a single 100 um thick LCP layer, as shown, mounted on a 200-400 um thick, FR4 grade printed circuit board (PCB) that contains all the digital signal processing and control signals. The LCP substrate 120 has a planar phased array beam-steering antenna array 105 printed on one side. The signals from each antenna 105 are RF transitioned to the backside with a 3D vertical transition 125. In the backside, the signals converge to the RFIC chip 115.
Although the foregoing prior art 3D integrated radar RF front-end system 100 is helpful in reducing the crosstalk between these types of transmission lines 110, additional improvements can be made to reduce the crosstalk between these types of transmission lines 110 as these lines converge towards the RFIC chip 115 on the backside. Also, additional improvements can be made to reduce the crosstalk between CPW interconnections or transmission lines. Therefore, a need exists in the art for an interconnection apparatus and method for low cross-talk chip mounting for automotive radars.